A method of forming a vacuum insulated refrigerator cabinet structure includes providing a multi-layer sheet of material comprising at least one layer of barrier material that is disposed between first and second outer structural layers. The barrier material and the first and second outer layers comprise thermoplastic polymers. The multi-layer sheet of material is thermoformed to form a non-planar first component having a central portion and four sidewalls extending transversely from the central portion. The method further includes securing a second component having a central portion and four sidewalls extending transversely from the central portion to the first component to form an interior space therebetween. Porous filler material is positioned in the interior space, and a vacuum is formed in the interior space. The first and second components are sealed together to form a vacuum insulated refrigerator cabinet structure.